In the subsequent description the expression “heterogeneous network” designates a network in which the transmission elements can be radio sets, satellites, etc.
In certain telecommunication applications, messages are transmitted to several recipients via heterogeneous networks (radio, satellites, etc.) while adapting to the terrain conditions (obstacles, propagation, movements of the nodes of the network) and while allowing robust and globally efficient service provision. Global efficiency is intended to mean a good ratio between the volume of information correctly transmitted and the spectral resources consumed. This is in particular manifested through:
utilization of the broadcasting capabilities of the medium,
minimization of the monitoring information (overhead and protocol exchanges).
The data transmission must also show its efficiency taking account in particular of the constraints listed hereinbelow:
the fluctuations of the transmission conditions are often much faster than the transmission delay of a message, messages of significant size, reduced bandwidth. The global efficiency is therefore also conditioned by the overhead of taking these changes into account, even for the already partially transmitted messages;
a message must be delivered within an allowed delay, whatever the recipient of the message. If reaching certain recipients makes it impossible to keep to this timescale, for example subsequent to degraded transmission conditions, this must not have any impact or must have little impact on delivery to the recipients for which the transmission conditions are nominal.
The NORM protocol known to the person skilled in the art (standing for “Nack-oriented reliable multicast”), RFC 5740, is used for point-to-multipoint data transmission. This NORM protocol adapts the volume of information to be transmitted or retransmitted as a function of the feedback of the receivers, through the use of negative acknowledgements.
The protocol known by the abbreviation PGM (Pragmatic Group Multicast) is a protocol for reliable multicast broadcasting of information generated automatically, in real time, between several sources and several receivers. It proposes data transmission of enhanced reliability in a tree monitored by a transmission window managed by the sender. It is addressed to applications that are insensitive to losses that are not corrected by the protocol. Indeed, only the information detected by the receivers as being lost is signaled, by negative acknowledgement. The sender is never certain that the receiver has received the entire message.
Patent application EP1989822 discloses multipoint transmission of enhanced reliability between a sender and several recipients. The reliability of the transmission is enhanced by introducing a server and point-to-point communications between the recipients in case of losses.
Other data transmission protocols such as network coding or random linear network coding known by the abbreviation RLNC (Random Linear Network Coding) are also known from the prior art.
Despite the advantages that they afford, most methods known from the prior art exhibit drawbacks in the deployments of heterogeneous networks. The methods of the prior art do not minimize the overheads related to the needless transmission of information, the useful information transmitted already being in the possession of the receiver or the volumes of monitoring information becoming significant relative to those of the information useful to the recipients.
The prior art does not address the problematic issue of forwarding on heterogeneous networks in multi-hop mode.
The Intra-stream “Network Coding” approach affords a noticeable improvement in resilience. The aforementioned RLNC approach consists of the random generation of the coding factors. Nonetheless, this approach exhibits the following drawbacks:                The probability of generating linearly dependent sequences is non-zero, redundant data are then sent needlessly over the medium, (non-deterministic code),        The necessity of transmitting the sequence's coding factors so as to allow its decoding, this incurring a resource consumption overhead,        The principles of partial recoding at the level of the relays, based on a partially received item of information which at this stage is undecodable, make it possible to generate only sequences that are linearly dependent on those already sent. This increases the probability of finding, at the destination, linearly dependent sequences and therefore of having sent needless information,        RNLC requires the use of end-to-end signaling making it possible to monitor the transmission when the recipient has received sufficient data for the decoding.        